DENVER—Recreational marijuana use became legal in Washington state Thursday, but Colorado could have to wait almost a month before the state constitution allows people to legally smoke pot in private.

Colorado’s elections chief planned Thursday to certify last month’s vote to allow recreational marijuana use. The certification sets up a 30-day window for Gov. John Hickenlooper to declare the amendment part of the state constitution.

A spokesman for the governor said Thursday there’s no date planned for Hickenlooper to make the declaration. The governor doesn’t have veto power of a voter-approved amendment, but state officials may be waiting for a response from the federal government before taking the final stop on marijuana legalization.

The governor’s spokesman, Eric Brown, has said Hickenlooper is assembling a task force to examine the marijuana change. Further details weren’t available Thursday.

Hickenlooper has until Jan. 5 to declare recreational marijuana part of the constitution. He could make the declaration out of public view at any point until then.

In Washington state, enactment of the marijuana law was set in statute by voters. Marijuana activists celebrated by counting down to midnight outside Seattle’s Space Needle and lighting up when the drug became legal. Though public use isn’t allowed in Washington, no criminal citations were issued.

Colorado’s measure allows adult over 21 to possess up to an ounce of marijuana, or six plants. Public use isn’t allowed.

Both states call for regulation of a commercial marijuana industry. So far the federal government has insisted marijuana remains illegal under federal law, but there’s been no word of lawsuits or other measures to block legalization in the two states.

“Neither states nor the executive branch can nullify a statute passed by Congress,” said a statement issued Wednesday by the Seattle U.S. attorney’s office.

Meanwhile, prosecutors across Colorado are grappling with how to handle cases involving possession of less than an ounce of marijuana. Prosecutors in several counties, including Denver and Boulder, have announced they will no longer charge those 21 and older with less than an ounce and also drop some or all pending cases.

“You cannot criminally prohibit behavior that about 50 percent of the populace believes should be legal,” Boulder District Attorney Stan Garnett said. “The system just collapses, it doesn’t work. That’s what’s happening with marijuana.”

But in some counties, including Weld and Jefferson west of Denver, prosecutors said they won’t drop such cases.

“Our job is to follow the law as it is now,” said Jefferson County District Attorney Scott Storey.

As news of the deadly mass shooting at Marjory Stoneman Douglas High School in Parkland, Florida, unfolded last week, Pia Guerra, a 46-year-old Vancouver-based artist, felt helpless. She couldn’t bring herself to go to sleep, so she began to draw.

Police who find suspected drugs during a traffic stop or an arrest usually pause to perform a simple task: They place some of the material in a vial filled with liquid. If the liquid turns a certain color, it’s supposed to confirm the presence of cocaine, heroin or other narcotics.